234 THE HISTORY OF SCIENCE 



observatory in Allegheny now a part of the city 

 of Pittsburgh. His chief apparatus was a whirling 

 table, sixty feet in diameter, and with an outside 

 speed of seventy miles an hour. This was at first 

 driven by a gas engine, ironically named " Auto- 

 matic," for which a steam engine was substituted 

 in the following year. By means of the whirling 

 table and a resistance-gauge (dynamometer chrono- 

 graph) Langley studied the effect of the air on 

 planes of varying lengths and breadths, set at vary- 

 ing angles, and borne horizontally at different veloc- 

 ities. At times he substituted stuffed birds for the 

 metal planes, on the action of which under air pres- 

 sure his scientific deductions were based. In 1891 he 

 published the results of his experiments. These proved 

 in opposition to the teaching of some very distin- 

 guished scientists that the force required to sustain 

 inclined planes in horizontal locomotion through the 

 air diminishes with increased velocity (at least within 

 the limits of the experiment). Here a marked con- 

 trast is shown between aerial locomotion on the one 

 hand, and land and water locomotion on the other ; 

 " whereas in land or marine transport increased speed 

 is maintained only by a disproportionate expenditure 

 of power, within the limits of experiment in such 

 aerial horizontal transport, the higher speeds are 

 more economical of power than the lower ones. 19 

 Again, the experiments demonstrated that the force 

 necessary to maintain at high velocity an apparatus 

 consisting of planes and motors could be produced 

 by means already available. It was found, for ex- 

 ample, that one horse-power rightly applied is suffi- 

 cient to maintain a plane of two hundred pounds in 



